Wiper for rotary electrodes



Se t, 30 51947.

WIPER FOR ROTARY ELECTRODES Filed June 18, 1943 56 000000 00000 00 0000000000000000000 000 0000 00000000000 y 00000000000000000 0000 00000000000000000 30 OOOOOOOOOOOOOOO 000000000000 0000000000 00039 oooooqoooo mm. make; 6 000 0000000000 00000000 7 0000000000 0 00000000000000 0000000000 oooqoooooo 00600 000000006 000000000 ogoooo o/ INVENTORSc/imonl H. B. JOHNSON ET AL 2,428,224

Patented Sept. 30, 1947 WIPER FOR ROTARY ELECTRODES Herbert B. Johnsonand Ralph H. Johnson, Rochester, N. Y., assignors to Ritter ProductsCorporation, New York Rochester, N. Y., a corporation of ApplicationJune 18, 1943, Serial No. 491,347

8 Claims. -(ci. 15-2565) This invention relates to wipers for cleaningrotary electrodes such as employed in electrostatic separation apparatusand, more particularly, to improvements in the construction andcomposition of such wipers for increasing the operating efliciency anddurability of the wipers, and thereby promoting the operating efficiencyof the electrodes as well. One object of the invention is to provide animproved and more efficient wiper of the above character forcontinuously cleaning and polishing an electrode, to keep its surfacesmooth and free from projecting particles, or other surface portionstending to form spray discharge or sparking points such as would reduceits operating efiiciency.

Another object is the provision of such a wiper capable of effectivelypreventing the collection on the electrode of contaminating films orcoatings tending to insulate the electrode from electrical contact withthe materials to be separated and thereby reduce or destroy theiroperating efficiency.

Another object is to afford a wiper capable of operating with a minimumof frictional drag on the electrode, and thereby avoiding breakage ofits porcelain insulating mountings, as well as excessive consumption ofpower for rotating it.

Another object is to supply a type vor wiper adapted to prevent theformation on the electrode of films or coatings capable of retainingparticles of material so as to form sandpaper surfaces such as tend torapidly destroy wipers as hereto fore constructed.

A further object is to provide a more durable wiper oi the characterindicated and reduce the expense of frequent replacements.

To these and other ends the invention resides in certain improvementsand combinations of parts, all as will be hereinafter more fullydescribed, the novel features being pointed out in the claims at the endof the specification.

In the drawings:

Fig. 1 is an elevation, partly diagrammatic in character, illustratingthe action of a pair of separating electrodes of an electrostaticseparation apparatus and the application to such electrodes of wipersembodying the present invention;

Fig. 2 is an enlarged, perspective view of the main body portion of oneof said wipers;

Fig. 3 is an enlarged, sectional view tially on the line 3a-3a in Fig.2;

Fig. 4 is a similar, sectional view, but showing additional supportingmeans for the wiper, and

substan- Fig. 5 is a sectional elevation of a molding apparatus forforming said wipers.

United States patents, Nos. 2,135,716, granted Nov. 8, 1938, and2,258,767, granted October 14, 1941, to Herbert B. Johnson, describeimprovements in electrostatic separation methods and apparatus,comprising the important use of wipers for continuously maintainingclean, smooth and polished surfaces on the separating electrodes. Suchapparatus, as illustrated in Fig. 1 of the present drawings, commonlyincludes one or more pairs of spaced, cylindrical, metal electrodes l0and Il, each rotatably mounted at its ends on suitable bearingscomprising insulating porcelain parts. These electrodes are connectedacross a suitable source of high voltage current so as to give th'emhigh potential charges ofoppo site polarity, as indicated by the plusand minus signs, and to create an electrostatic field in the air gapbetween them.

The material l2 to be separated, in finely divided form, is suppliedfrom any suitable hopper l3, so as to be fed in a thin layer to the topof electrode 1,0 which rotates in the direction -indicated by thearrows, so as to convey the material through the'electrostatic field inthe gap between the electrodes. At 14 is a partition 0r dividerextending below and longitudinally of the electrode and includingsuitable containing means on either side, as l5, for separatelycollecting or otherwise disposing of the separated materials. As wellunderstood in the art, materials of different kinds are differentlyresponsive to the influence of the electrostatic field. Thus, particlesof some materials which are less responsive tend to drop vertically bygravity, as at It, and fall on one side of divider M, while particles ofother kinds take up a modified charge of such a character that they arerepelled from the negatively ch'arged conveyor electrode 80, toward thepositively charged electrode I I, and are separated and fall on theother side of divider M, as at Ill.

It is important in the operation of such apparatus that the electrodesurfaces be kept clean, smooth and polished to prevent the adherencethereto of particles of material or the development of other uneven orrough surface conditions tending to form sparking or spray dischargingprojections acting to adversely affect the charges intended to beinduced in the materials to be separated and the proper operation of theelectrodes. The maintenance of clean electrode surfaces is importantalso for the purpose of maintaining good electrical contact between thematerials and the electrode surfaces, as, for example.

grounded electrode, as indicated at i8, and the' trode II, as indicatedat ticles tend to form spray i9. Such adhering pardischarge and sparking.Yproje'ctions which seriously impair the operating efllciency of the.apparatus.

Such separating methods, furthermore, are frequently carried out underconditions in which the electrodes tend to acquire contaminating filmsor coatings, asmore particularly described hereafter, in which theadhering particles of material become imbedded and tenaciously retained.

Thus, many electrostatic separation processes are encountered, such, forexample, as disclosed in United States patent No. 2,197,865, to HerbertB. Johnson, involving the treatment of flotation concentrates comprisingparticles of materials having their surfaces coated with variousreagents used in the flotation process. Other processses involve thepretreatment and conditioning of the materials to be, separated withsuit-v able reagents for affecting their response to the action of anelectrostatic field. In separating materials carrying such reagents,especially while they are cooling and separating after being heated anddried, fumes and vapors from such reagents frequently cause, a coatingto be deposited on the charged electrode and also in some cases on thematerial conveying electrode. This coating is usually of gummy, stickynature, and may build up in time to a thickness of s to of an inch,thereby completely covering and' insulating the electrode SllLl'fB-OG.

The finer particles of the materials which tend to collect on theelectrodes are frequently hard minerals such as quartz. and if suchfilms or coatings are allowed to cover the electrodesurof materialbecome imbedded and retained, so that the electrode surface takes on thecharacter, more or less, of a"sandpaper surface which rapidly abradesand destroys the wipers. This excessive wear on the wipers is at timesaccelerated by the action of the same vapors or fumes which form thecoatings referred to, since these fumes tend, at their temperature rangeof between 100 and 600 F., .to penetrate fibers or fabrics of ordinarywipers and disintegrate. The electrode, surfaces may become so rough asto produce a strong, frictional resistance in contact with the wiperssufficient at times to break the porcelain elements by which theelectrode bearings are insulated, so that the 06 development of suchconditions involves excessive replacement of parts and attendantexpense.

We have found that these dimculties may be successfully overcome and amuch more efficient wiper provided by constructing the wiper body of aspecial composition comprising a compact, felted mass of fine metallicfibers coated with a binder which is adapted to be cured, solidified andhardened to unit the more conductive particles to the chargedelecasbestos or the like, or

rigid body capable of being molded or machined to desired size andshape. The mass of metal fibers forming the main constituent of thiscomposition is preferably a metallic wool such, for example, as theknown steel wool of commerce, except that we preferably employ thecommercially available long-fiber steel wool, the fibers of which aregraded as coarse, medium or fine, as conditions may indicate, and havinga length up to twenty feet. While steel wool is preferred for mostinstallations, we may employ fibers of copper or other metal bestadapted to supply a definite polarity-charge through frictional contactwith the particles to be separated, or in conjunction with theparticular metal of the electrode surface, as we find that there is adefinite relationship between the behavior of the particles to beseparated and the metal of the electrode surface, as well as the kind ofmetal of which the wiper fibers are made, involving the advantages ofboth natural contact potentials and also special superimposed chargeswhich may be selectively applied.

The felted mass of metal fibers or metal wool, preferably in the form ofa strip of the approximate length of the wiper, is saturated with asuitable plastic bonding material, such as shellac, gums, Bakelite,sodium silicate or other resins and molding compounds derived fromphenol, cresol, or xylenol and formaldehyde, phenolicmixtures thereofwhich are adapted, on curing. to solidify and unite the metal fiberstogether in a substantially rigid body, capable of being molded ormachine out to definite cross-sectional shape. Such binders, it will benoted, are generally resistant to acids.

After first saturating the metal wool strip, which is to form a wiper,we prefer to press out excess binder by passing the strip betweenrollers until the retained binder forms, say, seven to ten per cent byweight of the composition. After such pressure, the strip is molded toshape and cured under pressure in a suitable mold. Such a mold maycomprise, for example, a metallic tube portion 2 i Fig. 5, havingapproximately the same outer diameter as the electrode with which thewiper is to be used. To the opposite sides of the tube ii are securedwalls 22, of wood or other suitable material, to provide, with the tube2|,

fees. h y f r a ma i i which t pa ti s so mold cavities 2: correspondingto the desired cross-sectional shape of the wiper body, the surfaces ofthe tube forming the bottoms of the cavities being perforated, as shownat 24, for supplying the heated air, or other curing medium,

to the material in the mold.

cause them to o are U -shaped clamps Each mold cavity, after insertionof the wiper composition, is closed by a somewhat convex metal plate 25,which is formed with closely arranged perforations 26, as shown. Theplates 25 preferably pressed into the mold cavities, to compress thewiper composition, as by means of any suitable clamps (not shown) ,afterwhich rigid, 21 are fitted over the plates 25, as shown, to hold themand the wiper body under suitable compression. Such compressionpreferably causes some of the binder to exude into, or through theopenings 26 of plate 25, to more securely bond the plate to the wiperbody. Air or other gas is then supplied by any convenient means to theinterior of tube 2 I, at any suitable fibers in asubstantially so tocure, solidify and harden the binder. When ported by angular metalstraps 33 trode surface is maintained free the binder is cured, the moldis opened and the wiper body with its reinforcing backing plate 25 isremoved in permanently set, cross-sectional shape with one surface 28shaped or curved to conform to the surface of the electrode with whichthe wiper is to be formed as a compact felted mass of metal fibers andbinder united in a substantially rigid body with one face shapedfor.close wiping contact with the rotary electrode surface.

The means for supporting the wiper in place preferably comprises aplurality of threaded posts 29 fixed to the backing plate 25, to whichis preferably fitted a heavier and rigid supporting bar 30 ofsubstantially the same shape as the plate 25 so as to lie closelyagainst the same. Posts 29 project through openings in the bar 30 andare secured therein by nuts 3! and washers 32. The supporting bar 30 isprovided at its ends with suitable terminal brackets (not shown) ofporcelain, metal or the like, as desired, or it may be sup- (Fig. 1),secured thereto by the nuts ill and supported at their opposite ends, asby attachment to the hopper l3, as shown.

The multiplicity of metal fibers projecting at the contact surface offersharp, cutting edges in substantially point contact with the electrodesurface, progressively changing with thewear of the wiper surface .andoperating to effectively scrape, clean, smooth and polish the electrodesurface, without grooving the same, although, if desired, the wiper maybe given an oscillating endwise movement to equalize its wear, asdescribed in the above patent No. 2,258,767.

The rigid wiper body maintains its predetermined shape and close contactwith the electrode surface and removes all of the fine particles ofmaterial collected on the electrodes, as indicated in Fig. 1. The pointcontacts of the metal fibers serve to intensively scrub and clean theelectrode surface, so as to prevent the building up thereon of any filmor coating. The wiper composition is not subject to chemical attack byfumes or vapors emanating from the materials to be separated, and issufiiciently tough and resistant in character to avoid any appreciablewear by the particles adhering to the electrode,

6 used. The body 2.0 is thus appreciable wear and with a. reduction inthe power consumed in driving the electrodes of approximately 80%.proved cleaning and polishing of the electrodes has been found toincrease their separating efliciency by from 10% to 12%.

While we have described our invention herein in connection with the.details of a preferred embodiment, it is to be understood-that suchdescription is intended to be merely illustrative, rather than limiting,as it is contemplated that various modifications. in composition andconstruction of the wiper will readily occur to those skilled in sothat. such wipers have been found to be highly durable and economical inuse. Since the elecof any film or coating, the braking action, orfrictional resistance, of the wiper remains low, as well as the horsepower required for driving the electrode, and no undue strain is appliedto the mountings of either the electrode or the wiper itself.

Depending upon the nature of the reagents or other materials used forcoating the particles of material to be separated, or other specialconditions, we prefer, in some cases, to use a binder for the metal woolcontaining suitable percent ages of abrasive material, natural orartificial, such as powdered carborundum or silicon carbide, or garnetemery, or the like. On the other hand, we prefer in some cases tocombine with the binder of the wiper body a lubricating material such asgraphite, mica, vermiculite, soapstone, and the like, in relativeproportions, depending upon the conditions of particular applications.Thus, we have found that one half pound of powdered or flaked graphiteto three gallons of shellac provides a successful binder for many uses.

For the purpose of increasing the point contacts of the wiper fiberswith the electrode sur- 7 the art within the spirit of the invention andthe scope of the appended claims.

We claim:

1. A wiper for a rotary, cylindrical electrode of an electrostaticseparation apparatus, said wiper having a body comprising as its mainconstituent by weight a compact felted mass of fine, metallic fibers,together with a binder of a material which is substantially unaffectedby temperatures up to 250 F. and is relatively inert to chemical attack,said binder coating and uniting said fibers to form a substantiallyrigid body of predetermined shape and low frictional resistance, andmeans for supporting said body for wiping contact with said rotaryelectrode.

2. A wiper for a, rotary, cylindrical electrode of an electrostaticseparation apparatus. said wiper having a body comprising as its maincon stituent by weight a compact mass of metal wool. together with abinder of material other than rubber and which is relatively inert tochemical attack, said binder coating the fibers of said wool and unitingsaid fibers in a substantially rigid sistance, said body cylindricalelectrode of an electrostatic separation apparatus, said wiper having abody comprising as its main constituent by weight a compact felted massof fine metal fibers, together with a binder other than rubber coatingsaid fibers and containing a finely divided abrasive material, saidbinder being solidified to unite said fibers and material and provide asubstantially rigid body of elongated shape having a face thereof shapedto conform to a portion 'of the circumference of said electrode, andmeans for supporting said body with said face in longitudinallyextending, wiping contact with said electrode.

4. A wiper for a rotary, cylindrical electrode of an electrostaticseparation apparatus, said stituent by weight a compact mass of metalwool, together with a binder coating the fibers of said wool andcontaining a finely divided, lubricating material, said binder beingsubstantially unafiected by temperatures up'to 600 F. and being At thesame time, the imsolidified to unite said ilbers and material and iorm asubstantially rigid body oi elongated shape having a lace thereof shapedto conform to a portion oi the circumference of said electrode extendinglongitudinally thereof, and means for supporting said body with saidrace in longitudinally extending, wiping contact with said electrode.

5. A wiper for a rotary, cylindrical electrode of an electrostaticseparation apparatus, said wiper having a body comprising as its mainconstituent by weight a compact mass of steel wool, together with abinder of material which is substantially unaffected by relatively hightemperatures or by chemical attack, said binder coating the fibers ofsaid wool and being solidified to unite the same in a substantiallyrigid body of elongated shape, said body having a face thereof curved toconform to, a portion of the circumference of said electrode, a backingmember attached to an opposite face of said body for reinioreing andholding the same, and means on said member for attaching the same to asupport.

6. A wiper for a rotary, cylindrical electrode of an electrostaticseparation apparatus, said wiper having a body comprising as itsmainconstituent by weight a quantity of fine metallic fibers matted togetherin a compact felted mass together with a binder of a, material which issubstantially resistant to high temperatures and to chemical attack,said binder coating and uniting said fibers in a substantially rigid,elongated body of uniform cross-sectional shape and having a, surfaceshaped to conform to a portion of the circumference of said electrode, abacking member attached to said body for reinforcing and holding thesame, and means on said member for connecting the same with a support.

'l. A wiper for a, rotary, cylindrical electrode of an electrostaticseparation apparatus, said wiper having a body comprising as it's mainconstituent by weight a quantity of fine metal fibers closely mattedtogether in a compact, dense mass together with a binder of a materialother than rubber and which is substantially resistant to hightemperatures and to chemical attack, said binder coating said fibers andsolidified to unite the same in a substantially rigid, elongated body ofuniiorm cross-sectional shape and having a face thereof shaped toconform to a portion of the circumference of said electrode, aioraminous, metallic backing member having openings therein penetratedby said binder to secure said member to said body, and means on saidbacking member for connection with a support.

8. A wiper for a, rotary, cylindrical electrode of an electrostaticseparation apparatus, said wiper having a body comprising as its mainconstituent by weight a compactly matted, dense shellac binder coatingthe fibers of said wool and uniting the same in a substantially rigid,elongated body, said body having a face shaped to engage a portion ofthe circumference of said electrode, a foramlnous, metal backing memberhaving openings therein penetrated by said binder to secure said memberto said body, and means on said member for detachably connecting thesame with a support.

HERBERT B. JOHNSON. RALPH H. JOHNSON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

